The instant invention relates to a process for piecing yarn in an open-end spinning device, in which the yarn is fed back to the spinning device either from a winding device, in which it has first been wound up on a bobbin during the spinning process, or from a special piecing bobbin, as well as to a device for carrying out this process.
In open-end spinning machines, yarn breakage caused by plant trash particles such as husk parts, etc., in the fiber sliver occur from time to time and must be repaired. This is accomplished, by having the end of the broken yarn fed back from the bobbin to the spinning device where it is combined with the fibers fed to a fiber collecting surface.
Another situation occurs when the bobbin is to be replaced. In that case, piecing is carried out in the same manner as for a yarn breakage, by feeding the broken yarn back from the bobbin before replacement of the full bobbin by an empty bobbin tube, or by using an auxiliary yarn which is drawn from a special piecing bobbin. The piecing yarn is cut in the course of the piecing process, whereby the yarn section connected to the newly spun yarn and containing the piecing joint is severed from the subsequently delivered, newly spun yarn end is removed, and the subsequently delivered yarn is fed to the new former (See EP-OS 0.106.809). In order to achieve controlled piecing joints, the piecing yarn is inserted immediately into the pair of draw-off rollers when it is fed back and drawn off by the latter at production speed.
During piecing the yarn is subjected to very high acceleration, so that when high production speeds are used many yarn breakages occur or piecing becomes entirely impossible. Since the draw-off rollers are in proximity of the fiber collecting surface the twist imparted to the piecing yarn can distribute itself over only a short length of yarn so that over-twisting of the yarn can easily occur. This is yet another reason why the known device tends to cause yarn breakage. Since, as a rule, many identical spinning devices are installed next to each other in today's open-end spinning machines, a lowering of the speed is possible only for all adjoining spinning devices in common, and this has negative effects upon the yarn produced, and upon the quantity produced.